The present invention relates to latices of heterogeneous polymeric particles. Particles of such polymers may have clear and distinct zones of differing polymer structure as in the case of core/shell particles, or particles with an incomplete shell (continents). In some cases there is no distinct sharp dividing line between one polymeric structure and another; rather, there is a continuous gradual change in polymer composition between two loci on a polymeric particle. It is believed that such a gradual change may occur for a number of reasons such as the solubility of monomers in a polymeric particle, or the gradual change in the composition of a monomer increment over time such as going from a high to low styrene content.
In recent years there have been a number of patents directed to latices of heterogeneous polymeric particles. Such polymers have the potential to be tailored to specific end uses. It has been found that latices of polymers having substantially similar bulk compositions may behave in different manners depending upon the structure within the polymer particle.
Belgium Pat. No. 893,722 issued Jan. 3, 1983 in the names of A. R. Sinclair and E. H. Gleason assigned to Polysar International S.A., discloses a latex of a structured particle having a core of about 60 to 40% by volume of the particles comprising 55 to 65 parts by weight of a monovinylaromatic monomer; 45 to 35 parts by weight of a diolefin; 0.5 to 5 parts by weight of an ethylenically unsaturated acid, and 0.5 to 5 parts by weight of a primary amide or N-methylolacrylamide; and a shell comprising 40 to 60% by volume of the particles comprising 75 to 85 parts by weight of a monovinylaromatic monomer, 25 to 15 parts by weight of a conjugated diolefin, 0.5 to 5 parts by weight of an ethylenically unsaturated carboxylic acid and 0.5 to 5 parts by weight of a primary amide or N-methylolacrylamide. Papers coated with such latices have an improved gloss and pick.
European Patent Application No. 0 040,419 in the name of D. I. Lee and T. Mundorf, assigned to The Dow Chemical Company published 25.11.81, also discloses latex of structured polymeric particles. The particles comprise from 20 to 45 parts by weight of a soft domain comprising 25 to 65 weight percent of a monovinylidene aromatic monomer, and from 75 to 35 weight percent of a conjugated diolefin; and from 55 to 80 parts by weight of a hard interpolymer comprising from 70 to 90 weight percent of a monovinylidene aromatic monomer and from 10 to 30 weight % of an aliphatic diene monomer.
U.S. Pat. No. 4,134,872 issued Jan. 16, 1979 in the name of D. I. Lee assigned to the Dow Chemical Company, discloses a similar type of structured polymeric particle except that both the core and the shell contain carboxylic acid monomers.
Rohm & Haas Company have patents covering multi-component structured polymers. Much of this work is directed to polymers consisting mainly of acrylic acid or acrylate esters. Minor components in such systems include grafting agents such as alkyl esters of a,b-ethylenically unsaturated acids, active crosslinking agents such as glycols, or amides, and latent crosslinking agents such as carboxylic acids. Canadian Pat. No. 916,340 issued Dec. 5, 1972 and U.S. Pat. No. 4,107,120 issued Aug. 15, 1978 are representative of such art.
Rhone-Poulenc Industries have patents to latices of grafted copolymer latices for use in the manufacture of non-wovens. The novel component in the Rhone-Poulenc patent is bis(2-chloroethyl) vinylphosphonate. European Patents Nos. 52,562 and 52,561 are representative of this art.
None of the above art contemplates using alkenyl nitriles as a monomer. In the present invention the second domain contains from 1 to 20% of an alkenyl nitrile.
Paper manufacturers are seeking a latex binder which will provide a good balance of properties including good wet and dry pick, and acceptable paper stiffness at a low price. Unfortunately, these desiderata place conflicting demands on the latex manufacturer. To improve stiffness and gloss requires an increase in the so-called hard monomers with a resulting decrease in the soft monomers which give binding and pick properties. At best the latex manufacturer tries to achieve a balance of properties.
Latices used in paper coating generally comprise a "hard" monomer and "soft" monomer. Properties such as gloss and stiffness are attributed to the hard monomers and obtained at the expense of properties associated with soft polymers such as wet and dry pick. It is desirable to provide a polymer which provides a better balance of properties in a paper coating.